Slide bearing for crankshaft of internal combustion engine

ABSTRACT

There is provided a slide bearing for a crankshaft of an internal combustion engine, having a pair of half bearings combined with each other to form the slide bearing, and a crush relief formed in each end portion region in a circumferential direction of an inner peripheral surface of each half bearing by reducing a bearing wall thickness over an entire width in an axial direction of the half bearing, wherein a relief depth RD which is a reduction amount of the bearing wall thickness of the crush relief is maximum at each end portion in the circumferential direction of the half bearing, and gradually decreases toward a center in the circumferential direction, and the relief depth RD is maximum in a center in an axial direction of the half bearing, and gradually decreases toward both end portions in the axial direction.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a slide bearing for a crankshaft of aninternal combustion engine, which slide bearing is configured into acylindrical shape by combining a pair of half bearings.

2. Description of Related Art

In general, a crankshaft of an internal combustion engine is supported,at each journal portion thereof, by a main bearing constituted of a pairof half bearings provided in a cylinder block lower portion of theinternal combustion engine. In order to lubricate the main bearing, alubricating oil is supplied by an oil pump into a lubricating oil grooveformed in a circumferential direction in a inner peripheral surface ofthe main bearing, through an oil gallery formed in a cylinder block walland a through-hole formed in a wall portion of the main bearing. Thecrankshaft also has a first lubricating oil passage which penetratesthrough the journal portion in a radial direction and of which both endopenings communicate with the lubricating oil groove of the mainbearing, a second lubricating oil passage which branches from the firstlubricating oil passage to extend through a crank arm portion, and athird lubricating oil passage which connected with the secondlubricating oil passage and penetrate through a crank pin in the radialdirection so that both ends thereof open on an outer peripheral surfaceof the crank pin, whereby the lubricating oil supplied into thelubricating oil groove of the main bearing is further supplied into alubricating oil groove formed in a circumferential direction on theinner peripheral surface of a connecting rod bearing for the crank pinportion of the crankshaft through the first lubricating oil passage, thesecond lubricating oil passage and the third lubricating oil passage(see JP-A-08-277831, for example).

At the time of initial operation of the internal combustion engine,foreign matters remaining in the lubricating oil passage, that is, swarfgenerated by metal processing at the time of cutting of the oil passage,molding sand at the time of molding and the like tend to mix into thelubricating oil which is supplied to the slide bearings for thecrankshaft such as the aforementioned main bearing and connecting rodbearing. In the case of the conventional slide bearings for an internalcombustion engine, these foreign matters accompany the flow of thelubricating oil on the bearings as the crankshaft rotates, but aredischarged outside the bearings together with the lubricating oilthrough a gap formed between the bearings and a shaft portion by crushreliefs, chamfers and the like which are formed in end portions in acircumferential direction of the bearings.

As shown in FIG. 12, the aforementioned crush relief corresponds to arelief space 84 formed by reducing the thickness of the wall portion inthe end portion region in the circumferential direction of a halfbearing 80 by a relief depth RD in the radial direction from an originalinner peripheral surface 82 (main circular arc) which is concentric withthe center of rotation, and the relief space 84 is formed for absorbingpositional displacement and deformation of butt end surfaces of the halfbearings which may occur, for example, when the pair of half bearingsare installed in the journal portion or the connecting rod of thecrankshaft. Accordingly, the position of the center of curvature of thebearing inner peripheral surface in the end portion region in thecircumferential direction of the half bearing in which the crush reliefis formed differs from the position of the center of curvature of thebearing inner peripheral surface (main circular arc) in the remainingregion (refer to SAE J506 (item 3.26 and item 6.4), DIN 1497, section3.2, JIS D3102). The crush relief has a relief length RL, which isexpressed as the height to an upper edge of the crush relief formationregion from a horizontal surface, measured when the half bearing isplaced so that both ends thereof in the circumferential direction areplaced on the horizontal surface as lower end surfaces, and the reliefdepth RD is formed so as to be gradually smaller toward a centralportion from the end portion in the circumferential direction of thebearing throughout the relief length RL.

In the conventional configuration, the relief length RL and the reliefdepth RD of the crush relief are constant along the entire half bearingin the axial direction (width direction) of the half bearing (seeJP-A-2008-095858, paragraphs 0043, 0045, 0047 and the like, andJP-A-2005-069283).

JP-U-04-063810 shows another configuration of the crush relief where therelief length RL and the relief depth RD are not constant along theentire half bearing in the axial direction.

BRIEF SUMMARY OF THE INVENTION

In the internal combustion engines of recent years, an oil pump has beenreduced in size for the purpose of reducing fuel consumption, andtherefore, the supply amount of the lubricating oil to the bearingsliding surfaces has been decreased as compared with the internalcombustion engines of the past. Accordingly, if the crush relief isformed as in the conventional bearing, foreign matters are dischargedfrom it, but since the leaking amount of the lubricating oil is large,insufficient supply of the lubricating oil to the bearing slidingsurface occurs.

FIG. 13 shows conventional oil flows, and when the relief length RL ofthe crush relief is constant in the axial direction, an oil flow FC inthe bearing center goes in a straight line across the crush relief withrelative rotation of the shaft and the bearing, but in an oil flow FS atthe end portion side in the axial direction, a flow FS' which isdischarged outside increases whereas a flow FS″ which goes in a straightline decreases, since the distance to the end portion in the axialdirection is short, and this makes it difficult to form a favorable oilfilm on the bearing inner peripheral surface.

As a countermeasure against oil leakage from the conventional crushrelief, if a crush relief non-formation region (which is formed by thebearing inner peripheral surface) is simply provided at both sides inthe axial direction of the crush relief to substantially close the gapbetween the shaft surface and the bearing inner peripheral surfaces, theoil leakage amount becomes small. In this case, however, there arisesthe problem that the foreign matters included in the oil are difficultto discharge. If a large number of foreign matters pass the crush reliefwithout being discharged to go in the flow FS″ direction of FIG. 13 andenter the bearing sliding surface, troubles such as seizure, wear andthe like are likely to occur in the sliding surface.

Accordingly, an object of the present invention is to provide a slidebearing such as a main bearing and a connecting bearing for acrankshaft, having an improved crush relief with a small oil leakageamount in order to promote oil film formation on a bearing slidingsurface and excellent dischargeability of foreign matters included inlubricating oil.

In order to achieve the aforementioned object, according to one aspectof the present invention, there is provided a slide bearing for acrankshaft of an internal combustion engine, including a pair of halfbearings combined with each other to form the slide bearing, and a crushrelief formed in each end portion region in a circumferential directionof an inner peripheral surface of each of the half bearings by reducinga bearing wall thickness over an entire width in an axial direction ofthe half bearing, wherein a relief depth RD which is a reduction amountof the bearing wall thickness of the crush relief is maximum at each endportion in the circumferential direction of the half bearing, andgradually decreases toward the center in the circumferential directionof the bearing half, while the relief depth RD is maximum in the centerin an axial direction of the half bearing of the bearing half, andgradually decreases toward both end portions in the axial direction ofthe bearing half.

The slide bearing according to the present invention is preferably madesuch that a relief length RL of the crush relief which is expressed as aheight from a horizontal surface to an upper edge of the crush relief onthe bearing inner peripheral surface measured when each the halfbearings is placed on the horizontal surface so that both end surfacesin the circumferential direction thereof become lower end surfaces ismaximum RL1 in the center in the axial direction, and a relief lengthRL3 of the crush relief in each position in the axial directionseparated from the center in the axial direction by a distancecorresponding to ¼ of the entire width in the axial direction of thehalf bearing is 60% to 90% of the maximum relief length RL1.

The slide bearing according to the present invention is preferably madesuch that the relief length RL1 of the crush relief in the center in theaxial direction of the half bearing is 3 mm to 15 mm, and a relieflength RL2 of the crush relief at each of the end portions in the axialdirection is 0.1 mm to 2 mm. Further, the slide bearing according to thepresent invention is preferably made such that the relief depth RD ofthe crush relief at each of the end portions in the circumferentialdirection of the half bearing is 0.01 mm to 0.05 mm in the centralportion in the axial direction, and is 0.005 to 0.02 mm at each of theend portions in the axial direction.

According to the present invention, the upper edge of the crush reliefmay be configured to draw an arc on the bearing inner peripheralsurface, or may be configured to be in a shape of a straight line on thebearing inner peripheral surface.

According to the slide bearing for a crankshaft of an internalcombustion engine having the improved crush relief of the presentinvention, foreign matters included in the lubricating oil can beproperly discharged, and the exhaust amount of the lubricating oil fromthe crush relief formation portion can be reduced. Thereby, oil filmformation on the bearing inner peripheral surface can be made favorablewhile the risk of troubles such as seizure, wear and the like of thesliding surface of the slide bearing is reduced.

Further, according to the slide bearing for a crankshaft of an internalcombustion engine having the improved crush relief of the presentinvention, when the lubricating oil which flows in the circumferentialdirection with relative rotation of the bearing and the shaft passes thecrush relief formation portion, the flows of the oil easily gathertoward the center in the axial direction, and thereby, the oil filmformation on the bearing inner peripheral surface can be made morefavorable. Further, since by the crush relief which has a preferablesize according to the present invention, the flows of the oil easilygather toward the center in the axial direction, but do not excessivelyconcentrate on the center, the oil does not have excessively highpressure in the center in the axial direction of the crush relief, andaccordingly, the slide bearing in which the flow of the oil in thecenter is not hindered is provided.

The other objects, features and advantages of the present invention willbecome apparent from the following description of the embodiments of thepresent invention relating to the accompanying drawings.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

FIG. 1 is a side view of a slide bearing having a crush relief accordingto one embodiment of the present invention;

FIG. 2 is a view of a half bearing of the slide bearing shown in FIG. 1seen from an inner peripheral surface side;

FIG. 3 is an enlarged side view of an end portion in a circumferentialdirection of a half bearing of the slide bearing shown in FIG. 1;

FIG. 4 is a view of the end portion in the circumferential direction ofthe slide bearing shown in FIG. 3 seen from a rotation center side;

FIG. 5 is an enlarged view of the end portion in the circumferentialdirection of the half bearing shown in FIG. 2;

FIG. 6 is a view seen along the arrow X of a joint portion of the slidebearing shown in FIG. 1 seen from the rotation center side;

FIG. 7 is a schematic view for explaining flows of oil between a crushrelief formation portion of the slide bearing and a shaft;

FIG. 8 is another schematic view for explaining the flows of oil betweenthe crush relief formation portion of the slide bearing and a shaft;

FIG. 9 is a view of the end portion in the circumferential direction ofthe slide bearing according to the present invention seen from therotation center side, similar to FIG. 4;

FIG. 10 is an enlarged view of an end portion in a circumferentialdirection of a half bearing of a slide bearing according to a secondembodiment of the present invention;

FIG. 11 is a view of a joint portion of the slide bearing according tothe second embodiment of the present invention seen from the rotationcenter side;

FIG. 12 is an enlarged side view of an end portion in a circumferentialdirection of a half bearing in which a conventional crush relief isformed; and

FIG. 13 is a view of a joint portion of a slide bearing including theconventional crush relief shown in FIG. 12 seen from an inner peripheralsurface side.

DETAILED DESCRIPTION OF THE INVENTION Embodiment 1

FIG. 1 shows a slide bearing 10 including crush reliefs 12 according toone embodiment of the present invention. In this case, the slide bearing10 is a connecting rod bearing constituted of a pair of half bearings 14and 16, and is disposed between a connecting rod (not illustrated) and acrank pin portion 18 of a crankshaft of an internal combustion engine.An arrow A of FIG. 1 shows a rotational direction of the crank pinportion 18. A lubricating oil passage 20 is formed inside the crank pinportion 18, and lubricating oil is supplied from the lubricating oilpassage 20 to a bearing sliding surface. In FIG. 1, a gap between thecrank pin portion 18 and an inner peripheral surface of the slidebearing 10 is shown to be larger than an actual scale, but it should benoted that FIG. 1 is only a schematic view, and a person skilled in theart can actually select a suitable gap.

As is understood from FIGS. 2 to 5, the crush relief 12 is formed over awidth W of the bearing by reducing the thickness of a wall portion inthe region of the end portion in the circumferential direction of thehalf bearing 14 by a relief depth RD in a radial direction from anoriginal inner peripheral surface (main circular arc) 22 of the bearing.The relief depth RD of the crush relief 12 at the end portion in thecircumferential direction of the half bearing 14 is maximum (RD1) in thecentral portion in the axial direction, gradually decreases toward theend portion in the axial direction from the central portion, and becomesminimum (RD2) at the end portion in the axial direction (FIG. 5). Therelief depth RD gradually decreases toward the central portion in thecircumferential direction, and becomes zero at an upper edge 24 of thecrush relief 12 (FIGS. 3 and 4).

Further, as shown in FIGS. 3 and 4, a relief length RL of the crushrelief, which is the height from a horizontal surface H to an upper edgeof the crush relief 12 measured when the half bearing 14 is placed sothat both ends in the circumferential direction of the half bearing 14are placed on the horizontal surface H as lower end surfaces, is maximum(RL1) in the central portion in the axial direction, gradually decreasestoward the end portion in the axial direction from the central portion,and becomes minimum (RL2) at the end portion in the axial direction. Inthe case of the embodiment in which the relief depth RD of the crushrelief 12 is formed to draw an arc as shown in FIG. 5, the upper edge 24of the crush relief 12 is also configured to draw an arc on the bearinginner peripheral surface.

FIG. 6 is a view seen along the arrow X of the portion of the crushrelief 12 of the slide bearing 10 shown in FIG. 1 seen from the innerperipheral surface side, and the main flows of the lubricating oil areshown by the arrows of the solid lines, and partial flows are shown bythe dotted lines. The lubricating oil which is supplied to the slidingsurface of the bearing flows from the inner peripheral surface of thehalf bearing 14 of the upper side to the inner peripheral surface of thehalf bearing 16 of the lower side as the crank pin portion 18 of thecrankshaft rotates. At this time, lubricating oil FC which flows in thecentral portion in the axial direction of the inner peripheral surfaceflows toward the central portion of the inner peripheral surface at thelower side. After lubricating oil FS2 which flows on the end portionside in the axial direction of the inner peripheral surface passes theinner peripheral surface and edge portions of the crush relief 12, amain part flows to the central portion in the axial direction, and apart of it (FS2′) flows to the end portion side in the axial direction.Since the relief length RL and the relief depth RD thereof are maximumat the central portion in the axial direction of the bearing in thecrush relief 12, and gradually become smaller toward both end portionsin the axial direction of the bearing, the oil leakage amount from therelease portions of the crush relief 12 in both the end portions in theaxial direction is small at this time. Since the lubricating oil whichflows toward the central portion in the axial direction of the halfbearing 16 of the lower side flows toward the axial direction of thebearing while flowing on the inner peripheral surface of the halfbearing 16 of the lower side across the crush relief 12, the amount ofoil which is discharged from the axial end portion becomes small ascompared with the conventional flow (FIG. 13), and oil film formation onthe inner peripheral surface of the bearing becomes favorable. In thiscase, the foreign matters also flow to the end portion in the axialdirection in the region where the crush relief 12 is formed, by the flowFS2′, and can be discharged outside.

In the present embodiment, the relief length RL1 in the central portionin the axial direction of the crush relief 12 is preferably 3 to 15 mm,and this is similar to the size of the conventional relief length RLconstant in the axial direction, which is the relief length RL of theordinary crush relief formed in the conventional slide bearing. Thereason of this is that if the relief length RL1 is less than 3 mm, inthe event when the positions of the end surfaces in the circumferentialdirection are displaced by combining a pair of half bearings and a leveldifference occurs on the inner peripheral surface side of the bearing,the effect of mitigating oil film breakage caused by this leveldifference becomes insufficient. Further, the reason why the relieflength RL1 is set at 15 mm or less is that if the relief length RL1 ofthe crush relief is made excessively large, the area of the innerperipheral surface of the bearing which receives load from thecrankshaft becomes small.

Meanwhile, a relief length RL2 at the end portion in the axial directionof the crush relief 12 is preferably 0.1 to 2 mm. The relief length RL2at the end portion in the axial direction of the crush relief 12 ispreferably made as small as possible, as long as foreign matters aredischarged, in order to reduce the oil leakage amount from the endportion in the axial direction of the bearing.

Further, a relief depth RD 1 in the central portion in the axialdirection of the crush relief 12 in the end portion in thecircumferential direction of each of the half bearings is preferably0.01 to 0.05 mm, and this is similar to the size of the conventionalrelief depth RD of the ordinary crush relief formed in the conventionalslide bearing which depth RD is constant in the axial direction. Thereason of this is that if the relief depth RD1 is less than 0.01 mm, inthe event when the positions of the end surfaces in the circumferentialdirection are displaced by combining a pair of half bearings and a leveldifference is formed on the inner peripheral surface side of thebearing, the effect of mitigating oil film breakage caused by the leveldifference becomes small. Further, if the maximum relief depth RD1 ofthe crush relief 12 in the end portion in the axial direction issuitable as shown in FIG. 7, the lubricating oil between a bottomsurface 50 of the crush relief 12 and a counterpart shaft surface 52accompanying the surface of the shaft which is rotated is fed in thecircumferential direction as shown by the arrows, but if the counterpartshaft surface 52 and a bottom surface 50′ of the crush relief 12 areexcessively alienated as shown in FIG. 8, the action from thecounterpart shaft surface on the lubricating oil of the bottom portionbecomes small, the amount of the lubricating oil which flows to theinner peripheral surface (sliding surface) on the front side of thebearing decreases, and the amount of oil which leaks from the endportion in the axial direction of the bearing becomes large. Thus, themaximum relief depth RD1 of the crush relief is set at 0.05 mm or less,whereby the action from the counterpart shaft surface is exerted overthe entire lubricating oil between the bottom surface 50 of the crushrelief 12 and the counterpart shaft surface 52, and supply of thelubricating oil to the inner peripheral surface (sliding surface) on thefront side of the bearing becomes sufficient.

Meanwhile, a relief depth RD2 at the end portion in the axial directionof the crush relief 12 in the end portion in the circumferentialdirection of each of the half bearings is preferably 0.005 to 0.02 mm.The relief depth RD2 is preferably made as small as possible, as long asthe foreign matters included in the lubricating oil are dischargedoutside the bearing, in order to reduce the leakage amount of thelubricating oil. In this case, while the relief depths RD1 and RD2 ofthe crush relief 12 are partially overlapping in range, this is becausethe relief depth needs to be made larger when the inside diameter sizeof the bearing becomes larger, but it is obvious that the relief depthsRD1 and RD2 should be set so as to satisfy the formula of RD1>RD2 withinthe respective numeric value ranges.

In order to pass the lubricating oil which flows on the inner peripheralsurface of the half bearing 14 of the upper side toward the centralportion in the axial direction of the inner peripheral surface of thehalf bearing 16 of the lower side as shown in FIG. 6, a relief lengthRL3 of the crush relief in each position QP in the axial direction atwhich the distance from the end portion in the axial direction of thehalf bearing is ¼ of the length (width) W in the axial direction of thehalf bearing (more specifically, the central position QP between anaxial central position CP and an axial end position EP) is morepreferably 60 to 90% of the relief length RL1 of the crush relief in thecentral portion in the axial direction (FIG. 9). The reason of it isthat if the relief length RL3 is less than 60% of the relief length RL1,the crush relief steeply decreases in sectional area in the axialdirection in the inner peripheral surface of the half bearing 16 of thelower side, and therefore the pressure of the lubricating oil becomes sohigh at a tip end portion TP at the center in the axial direction of thecrush relief of the half bearing 16 of the lower side that thelubricating oil becomes rather difficult to gather to the centralportion, whereas if the relief length RL3 exceeds 90% of the relieflength RL1, the lubricating oil easily flows in the circumferentialdirection, and hardly flows toward the central portion.

Embodiment 2

FIGS. 10 and 11 show a slide bearing according to a second embodiment ofthe present invention. If the bottom portion of the crush relief 12 isformed in such a manner that the relief depth RD draws a straight lineas shown in FIG. 10, the upper edge 24 of the crush relief 12 is alsoformed into a straight-line shape in the inner peripheral surface of thebearing as shown in FIG. 11. In this case, however, it should be notedthat in order to pass the lubricating oil which flows on the innerperipheral surface of the half bearing 14 of the upper side toward thecentral portion in the axial direction of the inner peripheral surfaceof the half bearing 16 of the lower side, the relief length RL3 of thecrush relief in each of the axial position QP at which the distance fromthe end portion in the axial direction of the half bearing is ¼ of thelength (width) W in the axial direction of the half bearing is set at 60to 90% of the relief length RL1 of the crush relief at the centralportion in the axial direction.

In the above embodiments, it should be noted that the conventionallubricating oil groove which is formed in the circumferential directionof the bearing inner peripheral surface is not shown, or does not haveto be always formed. Further, the width dimension of the slide bearingis determined by the capacity of the internal combustion engine, andtherefore, does not have to be limited in the present invention.Furthermore, it is obvious that in the slide bearing, a conventionalchamfer may be formed at each edge portion, aside from the crush relief,for the purpose of facilitating manufacture and assembly.

The above description is made for several embodiments, but it is obviousto a person skilled in the art that the present invention is not limitedthereto, and various modifications and corrections can be made withinthe range of the spirit and accompanying claims of the presentinvention.

1. A slide bearing for a crankshaft of an internal combustion engine,comprising a pair of half bearings which are combined with each other toform the slide bearing; and a crush relief formed in each end portionregion in a circumferential direction of an inner peripheral surface ofeach of the half bearings by reducing a bearing wall thickness over anentire width in an axial direction of the half bearing, wherein a reliefdepth RD which is a reduction amount of the bearing wall thickness ofthe crush relief is maximum at each end portion in the circumferentialdirection of the half bearing, and gradually decreases toward the centerin the circumferential direction of the half bearing, while the reliefdepth RD is maximum in the center in an axial direction of the halfbearing, and gradually decreases toward both end portions in the axialdirection of the half bearing.
 2. The slide bearing according to claim1, wherein a relief length RL of the crush relief which is expressed asa height from a horizontal surface to an upper edge of the crush reliefon the bearing inner peripheral surface measured when the half bearingsis placed on the horizontal surface so that both end surfaces in thecircumferential direction thereof become lower end surfaces is maximumRL1 in the center in the axial direction, and a relief length RL3 of thecrush relief in each position in the axial direction separated from thecenter in the axial direction by a distance corresponding to ¼ of theentire width in the axial direction of the half bearing is 60% to 90% ofthe maximum relief length RL1.
 3. The slide bearing according to claim1, wherein the relief length RL1 of the crush relief in the center inthe axial direction of the half bearing is 3 mm to 15 mm, and a relieflength RL2 of the crush relief at each of the end portions in the axialdirection is 0.1 mm to 2 mm.
 4. The slide bearing according to claim 1,wherein the relief depth RD of the crush relief at each of the endportions in the circumferential direction of the half bearing is 0.01 mmto 0.05 mm in the central portion in the axial direction, and is 0.005mm to 0.02 mm at each of the end portions in the axial direction.
 5. Theslide bearing according to claim 1, wherein the upper edge of the crushrelief is configured to draw an arc on the bearing inner peripheralsurface.
 6. The slide bearing according to claim 1, wherein the upperedge of the crush relief is configured to be in a shape of a straightline on the bearing inner peripheral surface.